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Three Rules Suffice for Good Label Placement

Abstract

The general label-placement problem consists in
labeling a set of features (points, lines, regions)
given a set of candidates (rectangles, circles,
ellipses, irregularly shaped labels) for each
feature. The problem arises when annotating
classical cartographical maps, diagrams, or graph
drawings. The size of a labeling is the number of
features that receive pairwise nonintersecting
candidates. Finding an optimal solution, i.e., a
labeling of maximum size, is NP-hard. \par We
present an approach to attack the problem in its
full generality. The key idea is to separate the
geometric part from the combinatorial part of the
problem. The latter is captured by the conflict
graph of the candidates. We present a set of rules
that simplify the conflict graph without reducing
the size of an optimal solution. Combining the
application of these rules with a simple heuristic
yields near-optimal solutions. We study competing
algorithms and do a thorough empirical comparison on
point-labeling data. The new algorithm we suggest
is fast, simple, and effective.